The present invention relates to a thermosensitive image transfer recording medium capable of forming on a receiving sheet images having high image density, excellent image gradation and durability, with high thermal sensitivity by application of heat to an image transfer layer of the recording medium, for instance, through a thermal head or a laser beam application device so as to imagewise transfer a thermofusible ink composition contained in the image transfer layer to the receiving sheet, thereby recording images on the receiving sheet. The thermofusible ink composition comprises as the main components a colorant and a thermofusible wax material.
More particularly, the present invention relates to a thermosensitive image transfer recording medium comprising a support material and an image transfer layer formed thereon, which image transfer layer comprises (i) a fine porous network structure made of a resin comprising a cellulose acetate butyrate, (ii) a non-volatile oily material which is contained in the fine porous network structure, and which does not dissolve the resin of the porous network structure, and (iii) a thermofusible ink composition held in the porous network structure, which comprises as the main components a colorant, and a thermofusible wax material which is solid at room temperature.
Conventionally, there are known (i) a thermosensitive image transfer sheet comprising a support material and a sublimable dye layer formed on the support material, and (ii) a thermosensitive image transfer sheet comprising a support material and a thermofusible ink layer comprising a thermofusible material and a pigment which are homogeneously dispersed therein, capable of forming images on a receiving sheet by subjecting the thermosensitive image transfer medium to thermal printing.
The method using a sublimable dye, however, is superior in the reproduction of image gradation, but has the drawbacks that the thermal sensitivity is low and the durability of the reproduced image is poor. On the other hand, the method using a thermofusible material and a pigment is superior in thermal sensitivity and the durability of the produced images, but has the drawback that the image gradation is unsatisfactory.
Furthermore, there has been proposed a thermosensitive image transfer recording medium comprising a support material and a fine porous structure formed thereon, which contains a thermofusible ink composition consisting essentially of (a) a thermofusible material which is solid at room temperature and (b) a colorant. In comparison with the conventional thermofusible type recording mediums, the above proposed thermosensitive image transfer recording medium is improved on image gradation, but the image gradation obtained by this recording medium is not as good as that obtained by the recording medium using a sublimable dye.
Further, in the case of the above thermosensitive image transfer medium, when image transfer is performed onto a receiving sheet having high smoothness such as a receiving sheet made of synthetic paper or high quality paper, high image density and precise image gradation can be obtained. However, when image transfer is performed onto a receiving sheet having a rough surface, for instance, having a smoothness of 100 seconds or less, clear images cannot be obtained due to the rough surface of the receiving sheet, with the formation of non-uniform solid images and poor image gradation.